1. Field of the Invention
The present invention relates to a method of forming a metallization layer in semiconductor devices.
2. Discussion of Related Art
Generally, as for metallization materials in semiconductor devices, aluminum or aluminum alloy is widely used because aluminum has good conductivity and adheres well to silicon oxide. Aluminum is also easy to pattern by dry-etching, and is relatively cheap. This kind of metallization layer may make contact with a diffusion area, formed by doping impurity ions in a semiconductor substrate through a contact hole, or may make contact with a gate formed of polycrystal silicon, in which impurity ions are doped.
When the metallization layer made of aluminum or aluminum alloy makes contact with silicon, a silicon spike occurs at the junction between the metallization layer and the impurity region or gate during the heat-treatment process conducted after metallization. The spike decreases a breakdown voltage of the device including the impurity region or gate due to the centering of an electrical field, or the spike causes a leakage current flow at the junction.
To prevent the generation of the spike, a barrier metal layer is formed between the metallization layer and the impurity region or gate. The barrier metal layer prevents silicon of the semiconductor substrate or the gate from diffusing into the metallization layer during the heat-treatment process. Generally, when the metallization layer is formed of silicon-free pure aluminum or aluminum alloy, silicon of 0.4 to 0.7 wt % in the semiconductor substrate or the gate diffuses into the metallization layer during the heat-treatment process.
Another method for preventing the generation of the spike forms the metallization layer of aluminum or aluminum alloy containing silicon of 1 wt %. Here, the silicon in the metallization layer prevents the silicon of the substrate or the gate from diffusing into the metallization layer; thereby preventing the generation of the spike.
FIGS. 1A-1C illustrate this method for preventing the generation of a silicon spike. As illustrated in FIG. 1A, an insulating layer 13 is formed on a substrate 11 containing silicon. The insulating layer 13 is patterned by a typical photolithography process to form a contact hole 15 exposing the substrate 11. Alternately, the substrate 11 could represent a polycrystal silicon gate of a semiconductor device.
As illustrated in FIG. 1B, impurity ions of a conductivity type opposite to that of the substrate 11 are heavily doped on the portion of the substrate 11 exposed by the contact hole 15 to form a diffused region 17. However, if the substrate 11 is a conducting line made of polycrystal silicon, such as the gate of a semiconductor device, opposite conductivity type impurity ions are not doped therein.
As illustrated in FIG. 1C, aluminum or aluminum alloy containing silicon of 1 wt % is doped to make contact with the diffusion region 17 through the contact hole 15 by CVD or sputtering. The doped aluminum or aluminum alloy is patterned by photolithography to form the metallization layer 19. Here, after the aluminum or aluminum alloy is doped, it is heat treated at a temperature of 450 to 500.degree. C., so that the aluminum or aluminum alloy making contact with the substrate 11 realizes good ohmic contact. The silicon in the substrate 11 does not diffuse into the metallization layer 19 because of the silicon originally contained in the aluminum or aluminum alloy forming the metallization layer 19, and the spike is not generated.
In the above-mentioned conventional metallization layer forming method, aluminum or aluminum alloy containing silicon of 1 wt % is formed in contact with the diffusion region through the contact hole, and the substrate and the doped aluminum or aluminum alloy are heat-treated to realize an ohmic contact.
But, in the conventional method, silicon originally contained in the aluminum or aluminum alloy precipitates during cooling after the heat-treatment, and the precipitated silicon grows by using the substrate as a seed. As a result, the precipitated silicon reduces the junction area between the substrate and the metallization layer; thereby increasing the junction resistance.